Tailorable fiber-reinforced support structure for use in precision manufacturing

ABSTRACT

A fiber-reinforced support structure for use in precision manufacturing includes a composite housing having a core sandwiched between first and second groups of carbon-fiber reinforced layers. A plurality of cavities in the housing are provided for removably receiving inserts utilized to support components during precision manufacturing. Each of the cavities is lined with a carbon-fiber reinforced layer, and a protective ultraviolet-cured coating is provided on the exterior of the housing to prevent contamination in the manufacturing environment.

[0001] This invention was made with Government support under contractNo. DE-AC04-94AL8500 awarded by the U.S. Department of Energy. TheGovernment has certain rights in the invention.

FIELD AND HISTORICAL BACKGROUND OF THE INVENTION

[0002] The present invention is directed to a support structure, andmore particularly to a fiber-reinforced support structure for use inprecision manufacturing. The support structure is a composition that canbe tailored to match manufacturing requirements for coefficients ofthermal expansion, stiffness and dampening.

[0003] Demands for high precision in manufacturing systems has placedincreased performance demands upon subsystems, such as supportingstructure, control computers, and laser interferometers. The range ofapplications for computers and lasers far exceeds that of precisionsupport structures. As such, large companies with a vast engineeringinfrastructure tend to be the producers of high sales volume products,such as computers and lasers. Conversely, small companies tend to be theproducers of precision support structures, which have a limited demand.These small companies tend to have small engineering staffs and limitedanalysis capabilities. As a consequence, technological advances insupport structures have lagged behind the laser and computer industries.Accordingly, the support structure has become the critical,performance-limiting component in many precision manufacturing systems.

[0004] Recently, the requirements for increased stability has risen inapplications such as the high-speed manufacturing of very large flatpanel displays, as well as the manufacture of next generation integratedcircuits with feature sizes less than 0.1 micron. As a result, betterstructure materials are required for the supporting structures to meetthe future technological needs of the precision product industry, suchas the semiconductor industry.

[0005] Structure materials for the mechanical stages used to supportsilicon wafer during processing are one example where improvement isneeded. Semiconductor processing stages must be lightweight (to enhancerapid throughput), have good stiffness (to allow precision processing,such as for photolithography) and have a coefficient of thermalexpansion that matches with silicon (so no thermally imposed distortionsinfluence the precision processing).

[0006] Currently, aluminum and aluminum alloys are the most commonlyused stage material. However, aluminum is too dense (and therefore tooheavy), lacks the required stiffness when mass is minimized, and hasthermal expansion properties far greater than that of silicon.

[0007] It is extremely desirable for precision stage devices, such asmagnetically levitated photolithography machines, to possess acapability of high translation rates while maintaining a very high levelof accuracy. For optimal performance, the stage components should havelow weight for fast translation with minimal energy, high dampingcapacity to reduce the time for positional stability after translation(which is dependent on vibration dampening of the component), and higherresistance to non-steady-state distortion arising from any thermalinputs.

[0008] Various fiber-reinforced support structures are known and havebeen used in other industries. Representative examples include thefollowing U.S. patents: U.S. Pat. No. 4,680,216 to Jacaruso; U.S. Pat.No. 4,833,029 to DuPont et al.; and U.S. Pat. No. 6,051,302 to Moore. Ineach of the above examples fiber fabric is used to reinforce a honeycombcore structure.

[0009] U.S. Pat. No. 4,680,216 to Jacaruso teaches a single-layer fiberfabric reinforcement of a honeycomb core panel. In the preferredembodiment, the single-layer fabric is composed of graphite fibers wovenat a ±90° angle to each other.

[0010] U.S. Pat. No. 4,8337029 to DuPont et al. teaches a reinforcedhoneycomb facesheet where the reinforcement consists of a layer ofgraphite paper and a layer of loosely interwoven graphite fiber cloth onboth the top and bottom surfaces of the facesheet.

[0011] U.S. Pat. No. 6,051,302 to Moore teaches thermally conductive,nonmetal carbon pitch honeycomb panel reinforced by one layer ofperforated carbon fiber fabric on the top surface of the panel and a onelayer of nonperforated carbon fiber fabric on the bottom surface.

[0012] In view of the above, there remains a need in the precisionmanufacturing industry for a support structure material with a lowcoefficient of thermal expansion, sufficient stiffness to reducevibration, and of minimal weight. There additionally remains a need fora support structure material that can be specifically tailored to (1)reduce manufacturing processing times by decreasing stage translationtimes as well as the wait time for damping of structural resonances, and(2) reduce manufacture processing errors caused by thermal distortions.

OBJECTS AND SUMMARY OF THE INVENTION

[0013] The principal object of the present invention is to provide afiber-reinforced support structure for use in precision manufacturingwhich overcomes the drawbacks associated with conventional supportstructures.

[0014] An object of the present invention is to provide afiber-reinforced support structure for use in precision manufacturingwhich is made of a fiber-reinforced composite material comprised of alaminate of carbon-fiber reinforced epoxy skins covering an aramid fiberhoneycomb structure.

[0015] Another object of the present invention is to provide afiber-reinforced support structure for use in precision manufacturingwhich results in a weight reduction of more than 50%, compared to theconventionally used support structure materials, such as aluminum andaluminum alloys.

[0016] Yet another object of the present invention is to provide afiber-reinforced support structure for use in precision manufacturingwherein the composite structure can be tailored to reduce thecoefficient of thermal expansion to near zero compared with theexpansion of 25 ppm for aluminum (silicon is 6 ppm).

[0017] Still yet another object of the present invention is to provide afiber-reinforced support structure for use in precision manufacturingwherein the stiffness of the support structure is anisotropic, but canbe tailored so that it exceeds that of aluminum in the direction wherestrength is needed, i.e., in the x-y plane of the support structure.

[0018] An additional object of the present invention is to provide afiber-reinforced support structure for use in precision manufacturingwhich will maintain dimensional stability and lower mode harmonics,thereby allowing for quicker damping of vibrations after stagetranslation.

[0019] Yet an additional object of the present invention is to provide afiber-reinforced support structure for use in precision manufacturingwhich is easy to machine and inexpensive to produce.

[0020] In accordance with the present invention, a fiber-reinforcedsupport structure for use in precision manufacturing includes acomposite housing having a core sandwiched between first and secondgroups of carbon-fiber reinforced layers. A plurality of cavities in thehousing are provided for removably receiving inserts utilized to supportcomponents during precision manufacturing. Each of the cavities is linedwith a carbon-fiber reinforced layer, and a protective ultraviolet-curedcoating is provided on the exterior of the housing to preventcontamination in the manufacturing environment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other objects, novel features and advantages of thepresent invention will become apparent from the following detaileddescription of the invention illustrated in the accompanying drawings,in which:

[0022]FIG. 1 is a top perspective view of a fiber-reinforced supportstructure made in accordance with the present invention.

[0023]FIG. 2 is a bottom perspective view of FIG. 1.

[0024]FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 1;and

[0025]FIG. 4 is a schematic illustration of the sequence in which thefiber-reinforced layers are provided on a core.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The support structure in the form of a composite C is fabricatedby using a film epoxy adhesive to bond preferably 20 and 30 milgraphite/epoxy skins onto a core. As shown in FIG. 3, a preferably 1.25inch aramid honeycomb core 10 is provided. A plurality of graphite-epoxyunidirectional layers are then attached to the top and bottom surfaces12 and 14, respectively, by using an adhesive.

[0027] In particular, in one embodiment, a first graphite-epoxy layer 16is attached such that the fibers therein are oriented at 0° (shown byline 17 in FIG. 4). A second graphite-epoxy unidirectional layer 18 isthen placed over the layer 16, in a manner that the fibers therein areoriented 90° to the fibers in the layer 16 (see line 19 in FIG. 4). Athird graphite-epoxy unidirectional layer 20 is then placed over thelayer 18, in a manner that the fibers therein are oriented 45° from theorientation of fibers in the layer 18 (see line 21 in FIG. 4). A fourthlayer of the graphite-epoxy unidirectional layer 22 is then placed overthe layer 20, in a manner that the fibers therein are oriented generallyparallel to the fibers in the first layer 12 (see line 17 in FIG. 4). Afifth layer of the graphite-epoxy unidirectional layer 24 is then placedover the layer 22, in a manner that the fibers therein are oriented 45°from the fibers in the layer 22 (see line 23 in FIG. 4). Finally, thelast graphite-epoxy unidirectional layer 26 is placed over the layer 24,in a manner that the fibers therein are oriented 45° from the fibers inthe layer 24 (see line 19 in FIG. 4). In the same manner, the bottomsurface 14 is provided with, preferably six graphite-epoxyunidirectional layers to complete the basic composite structure. Thegraphite-epoxy layers are attached to the honeycomb core 10 using thestructural adhesive film and compression.

[0028] As shown in FIGS. 1 and 3, cavities 28 are then machined in thecomposite structure C. Preferably, cavities 28 are lined withgraphite-epoxy composite layers to provide a smooth bonding surface.Although not shown, the cavities 28 may be provided with screw-threadsthat correspond with the screw-threads in inserts 30. It is thus seenthat this composite structure C allows for easy incorporation of controlfeatures through rapid machining.

[0029] It is noted herewith that although square and octagonal cavitiesare shown, it is within the scope of this invention to provide cavitiesof different shapes and configurations, as desired. It is further notedherewith that although six layers of graphite-epoxy layers have beenshown to be provided on each of the upper and lower surfaces 12 and 14of the core 10, it is within the scope of this invention to provide moreor less layers, as desired to meet specific manufacturing applicationsand conditions. In addition, it is noted that the orientation of thefibers in various graphite-epoxy layers is varied by an angle between0-90°, preferably 45°. Although not shown, the graphite-epoxy layers arealso bonded to the sides of the core 10, to increase stiffness of thesupport structure and cover the exposed honeycomb surfaces. Finally, thecomposite C is sealed with a UV-cured epoxy to prevent any debris orother contamination in the manufacturing environment.

[0030] As described above in the preferred embodiment, the in-planeorientation of the composite support structure C of the invention hasthe minimum thermal expansion coefficient of about zero with a maximizedstiffness (in the same orientation) of 1.24×10⁵ MPa, almost double tothat of aluminum. The density of the composite support structure C isapproximately 0.55 g/cc, which is five times smaller than that ofaluminum. Table 1 compares the properties of an aluminum supportstructure with the composite support or structure C of the presentinvention. TABLE 1 Aluminum Composite of the Property (prior art)Invention % Improvement CTE (ppm) 25 ˜0 ˜100%    Stiffness (Mpa) 7 × 10⁴1.24 × 10⁵ 77% Density (g/cc) 2.69 0.55 87% Overall weight (lbs) 7.7 3.851%

[0031] While all the above properties are tailorable for the currentinvention, for the example of the preferred embodiment it can be seenthat the support structure of the present invention has significantlyimproved stiffness, lower density, and is about one-half in weight tothat of an identical support made of aluminum.

[0032] The coefficient of thermal expansion of the composite supportstructure C of the present invention is preferably variable (dependingupon the laminate structure chosen) and can be tailored from near zeroppm to almost any desired goal. Therefore, an exact match can be madefor the semiconductor or any other precision material that is beingprocessed.

[0033] In lithography for example, the 51% reduction in supportstructure weight allows for a corresponding improvement in processingspeeds. Likewise, the improved thermal stability allows for more overlayexposures and the higher internal damping allows for quicker vibrationssettling before wafer exposure.

[0034] One of the principal applications of this improved supportstructure is as a magnetically levitated stage for use inphotolithographic semiconductor wafer processing. Directly relatedapplications involve other stages to process semi-conductor materialswhere precise positioning, thermal stability, stiffness and low weightthroughput are critical. Other applications for the fiber-reinforcedcomposite support structure C of the present invention include anyvendors that supply photolithography equipment to the semiconductormanufacturers. This includes steppers, magnetically levitated stages oras a vacuum wafer chuck.

[0035] While this invention has been described as having preferredranges, steps, materials, or designs, it is understood that it iscapable of and designed for further modifications, uses and/oradaptations of the invention following in general the principle of theinvention, and includes such departures from the present disclosure, asthose come within the known or customary practice in the art to whichthe invention pertains and as may be applied to the central features setforth above, and fall within the scope of the invention and of theappended claims.

What is claimed is:
 1. A fiber-reinforced support structure for use inprecision manufacturing, comprising: a core having upper and lowersurfaces; a plurality of fiber-reinforced layers disposed on each ofsaid upper and lower surfaces; and at least one cavity extendingpartially through the thickness of said core and through thefiber-reinforced layers on one of said upper and lower surfaces forreceiving an insert to support a component used in precisionmanufacturing.
 2. The support structure of claim 1, wherein said corecomprises a honeycomb structure.
 3. The support structure of claim 1,wherein said core comprises an aramid fiber honeycomb structure.
 4. Thesupport structure of claim 1, wherein at least one of saidfiber-reinforced layers comprises a carbon fiber-reinforced epoxy layer.5. The support structure of claim 1, wherein at least one of saidfiber-reinforced layers comprises a graphite fiber-reinforced epoxylayer.
 6. The support structure of claim 1, wherein said at least onecavity includes an internal lining comprising a graphitefiber-reinforced epoxy layer.
 7. The support structure of claim 1,wherein: said core comprises side surfaces; and said side surfaces areprovided with at least one of said fiber-reinforced layers.
 8. Thesupport structure of claim 1, further comprising a protective coveringof an ultraviolet-cured epoxy provided on the exterior of the supportstructure.
 9. The support structure of claim 5, wherein said graphitefiber-reinforced epoxy layer comprises a unidirectionally aligned fiberlayer.
 10. The support structure of claim 9, wherein a plurality of saidunidirectionally aligned fiber layers are superimposed so as to beoriented at an angle of 0°-90° from each other.
 11. The supportstructure of claim 10, wherein six of said unidirectionally alignedfiber layers are disposed on each of said upper and lower surfaces onsaid core.
 12. A fiber-reinforced support structure for use in precisionmanufacturing, comprising: a composite housing including a coresandwiched between first and second groups of carbon fiber-reinforcedlayers; a plurality of cavities in said housing for removably receivinginserts utilized to support components used in precision manufacturing;each of said cavities being lined with a carbon fiber-reinforced layer;and a protective ultraviolet-cured coating provided on the exterior ofsaid housing.
 13. The support structure of claim 12, wherein: one ofsaid first and second groups of carbon fiber-reinforced layers comprisesunidirectionally aligned graphite-fiber layers; and said graphite-fiberlayers are oriented at an angle of 0°-90° with respect to each other.14. The support structure of claim 13, wherein said one of said firstand second groups comprises six graphite-fiber layers.
 15. The supportstructure of claim 13, wherein said core comprises an aramid fiberhoneycomb structure.
 16. The support structure of claim 13, wherein saidgraphite-fiber layers are oriented at an angle of about 45° with respectto each other.